Preparation Technology And Microstructure Evolution Of Gas Film Holes In Turbine Blades

The nickel-based single crystal alloy is the main material on the turbine blade because of its excellent high temperature resistance,creep resistance and oxidation resistance.Processing a large number of thin film cooling holes on the aircraft engine can greatly improve the cooling characteristics of the cooling sheet,which can reduce the temperature of the engine box.However,processed cooling holes damage the workpiece material,thus affecting the life of the aircraft and increasing the manufacturing cost of the aero-engines.This paper mainly studies the macro and micro structure of the air membrane pores and the evolution of the structure of the turbine blades under high temperature conditions.Nanosecond laser punching and electric spark punching two processes are used,and the two are compared.Use test,literature and numerical simulation,and discuss the structure and the ratio of the film cooling hole and atoms.This paper mainly conducted the overall study from the following aspects:(1)Experiment of electric spark and nanosecond laser processing of nickel-based single crystal superalloy DD5,the results show that the average power has a significant effect on the processing of air membrane pores.As the average power increases successively,the lower aperture of the air membrane hole gradually increases and increases to a certain value remains stable.At this time,the diameter difference between the upper and lower holes will be smaller and smaller,resulting in the taper and roundness error of the air film hole will gradually decrease,making the air film hole closer and more round.The surface has microcracks,thermal influence area and ablation.The nanosecond laser-processed holes have a good surface quality.However,both processes will have a recast layer structure generation,and the hole wall part of the recast layer will produce oxygen elements.The oxygen element content of the electrospark and nanosecond laser hole wall is 8.49% and 4.78%,respectively,and obviously the electrospark oxidation is more serious.(2)Using secondary electron imaging by scanning electron microscope,it can be found that both the electric spark and nanosecond laser fabrication hole wall will be formed by recast layer structure,and the recast layer structure produced by nanosecond laser perforation is obviously different from that produced by electric spark.The use of electric spark punching will make the air membrane hole wall to produce columnar crystal,mainly striped,in the center of the column crystal will form a central coarse isoaxial grain,isoaxial crystal is mainly granular.Natosecond laser punching hole wall surface has the production of spinel phase and isoaxial crystal.In addition,an additional small number of butterfly-like cell crystals are produced.(3)High temperature aging treatment test shows that the aging treatment temperature will have a significant impact on the organization of the air film hole recasting layer.By comparing the morphology of the 1mm at 1000℃ 2h,1200℃ 2h and 1300℃ 2h,it can be concluded that the turbine blade has a larger phase size at1200℃ 2h and 1000℃ 2h.At 1000℃ 2h,the columnar crystal stripe of the pore wall becomes larger,and there are isoaxial crystals at the edge of the cylindrical crystal.At1200℃ for 2h,the isoaxial crystals gradually disappeared,while the column crystals became more and more compact,showing rafts compared with the matrix.Natsecond laser processing gas film pore wall has obvious carbide production on the spinel phase at 1000℃ 2h,the spinel phase width is about 2 m.At 1200℃ for 2h,the wider the spinel structure and isoaxial crystals are about 2.5 m.However,under 1300℃ 2h processing conditions,the material has an initial melting phenomenon,and the phase becomes irregular and irregular,and the matrix phase breaks.(4)The cooling efficiency of gas film hole structure is numerically simulated.The tilt angle and taper of gas film hole have great influence on the cooling efficiency.Compared with the tilt Angle of the air film hole and the cone Angle on the cooling characteristics of the film cooling hole,it is known that when the cylindrical air film hole and the bottom face wall surface are 30°,the cooling efficiency of the film cooling hole on the cooling wall is the best,and as the Angle increases,the cooling efficiency gradually decreases.In the range 5 <x / d <15,the cooling efficiency exceeds 45 and 60°;within 15 <x / d <30.Under the condition of the same inclination angle and the same upper aperture,the cooling efficiency of the film cooling hole decreases with the increase of the cone angle,and it is less than that of the cylindrical air film hole.